Spanner type wrenches, sometimes referred to as c-spanners, pin spanners, or hook spanners, generally consist of a handle section coupled to a curved arm, which can be fixed or pivotally articulated, and have an engagement feature on the end. These tools are commonly used to turn threaded features or other rotatable bodies which are of large diameter, require substantial torque, require many engagement positions, or are part of assemblies which extend for a significant length along the axis of rotation. This is especially true where the rotatable body is the same diameter or smaller than the diameter of the rotatable body assembly. In these cases, the ability to install the spanner along a vector, or series of vectors, substantially perpendicular to the axis of rotation is often required.
The use of spanner engagement features, such as radial holes or slots, is also beneficial in the design of rotatable bodies with space or strength constraints. These features often require less radial thickness and cross-sectional area than other common rotational engagement features, such as convex-polygonal sections, and offer superior torque transmission. It is also possible to increase the number of spanner engagement features with generally minimal impact on the torque capacity of the rotatable body. In contrast, typical convex-polygon sections generally decrease in torque capacity as the face count increases.
A traditional disadvantage of a spanner type wrench is the need to either rotate the tool completely around the rotational axis to provide continuing rotation of the rotatable body, or frequently reposition the engagement between the tool and the rotatable body. This repositioning is also more difficult than that of a tool, such as a box wrench, since the spanner must be properly positioned both rotationally and axially, relative to the axis of rotation, instead of only rotationally aligned. This often requires visual rather than tactile placement of the tool into the engagement features of the rotatable body. The alternative of rotating the tool completely around the axis of rotation is often not possible due to limited access to the rotatable body, or limited ability to rotate the tool, such as when the spanner must be positively retained with a safety cable. These limitations lead to substantial time being consumed repositioning the spanner, especially when a rotatable body requires many rotations or conditions hinder the repositioning process.
A spanner as suggested by U.S. Pat. No. 2,810,313 (1957) to Hermanson attempts to address some of these disadvantages by allowing the dogs that interact with the engagement features on the rotatable body to pivot. Despite this modification substantial functional limitations remain. This design still requires repositioning of the dogs on the tool into the next engagement feature on the rotational body in essentially the same fashion as a conventional spanner. The pivoting of the dogs also generally weakens their load carrying capability and requires a plurality of engagement features at specific positions on the rotatable body to function effectively. This design also requires either axial installation, or the placement of one dog followed by the rotation of the tool into engagement which utilizes a significant amount of the available rotational arc.
A need therefore exists for a tool providing the functional benefits of a spanner wrench which retains the ability to be installed along a vector substantially perpendicular to the rotational axis and which also allows continuous rotation of a rotatable body without continuous rotation of the tool or repositioning of the tool on the engagement features of the rotatable body.